The invention relates to amplitude and phase equalizers of analog or digital signals, such as useful in signal transmission or magnetic recording/reproduction and more particularly, to equalizers having a simplified circuit design and improved signal-to-noise ratio.
Prior art equalizers of signals passing through a recording or transmission channel for obtaining a desired amplitude characteristic and linear phase characteristic with frequency are susceptible to noise and signal distortion results. For example, equalizers having cascaded passive and active filter circuits whose combined frequency responses yield a desired amplitude and phase versus frequency characteristic over a known bandwidth are known to have a rather complex design including several consecutive stages, such as phase equalizer, low frequency pass, high frequency pass, line driver, etc. Each such stage comprises an active device with high impedance input and/or output circuit and therefore it is susceptible to noise. Such noise may originate from parasitic capacitance within the circuit or from an external power supply. Each consecutive stage further contributes to the noise, thus a low signal-to-noise ratio of the equalized signal results.